Hazard Assessment and Risk Analysis of Two New Synthetic Vitreous Fibers

• Published in: Regulatory toxicology and pharmacology Vol. 30; no. 1; pp. 54 - 74
• Main Authors: Maxim, L.Daniel, Mast, Richard W., Utell, M.J., Yu, C.P., Boymel, Paul M., Zoitos, Bruce K., Cason, James E.
• Format: Journal Article
• Language: English
• Published: San Diego, CA Elsevier Inc 01-08-1999; Elsevier
• Subjects: Animals; Biological and medical sciences; Calcium Compounds - toxicity; Carcinogenicity Tests; Carcinogens - pharmacokinetics; Carcinogens - toxicity; Chemical and industrial products toxicology. Toxic occupational diseases; Humans; Inorganic dusts (pneumoconiosises) and organic dusts (byssinosis etc.); Lung - drug effects; Lung - metabolism; Lung - pathology; Lung Neoplasms - chemically induced; Lung Neoplasms - pathology; Magnesium Oxide - toxicity; Medical sciences; Metabolic Clearance Rate; Mineral Fibers - toxicity; Oxides - toxicity; Pulmonary Fibrosis - chemically induced; Pulmonary Fibrosis - pathology; Rats; Risk Assessment; Silicon Dioxide - toxicity; synthetic vitreous fibers; Toxicology; vitreous fibers; Biodeterioration; Artificial fiber; Rat; Respiratory disease; Toxicity; Rodentia; Synthetic fiber; Harmlessness; Malignant tumor; Dissolution; Bronchopulmonary; Inhalation; Vertebrata; Chronic; Mammalia; Animal; Thermal insulating material; Interstitial pneumonitis; Glass fiber; Physicochemical properties
• ISSN: 0273-2300; 1096-0295
• DOI: 10.1006/rtph.1999.1314

Isofrax and Insulfrax are two new synthetic vitreous fibers (SVFs) developed for high-temperature insulation (1800–2300°F) applications. In an attempt to significantly reduce or eliminate the potential of adverse health effects, these two fibers were specifically designed to have high solubility and, thus, low in vivo biodurability. In this paper, we review the effects of chemical composition on biodurability, in vitro fiber dissolution rates (Kdis), and the relevance and relationship of Kdis to pulmonary fibrosis and lung tumors in chronic rat inhalation studies. We also examine the correlations between Kdis and weighted in vivo half-life (t0.5) of long fibers (>20 μm) and their relation to pulmonary effects in chronic rat inhalation bioassays. Predictions for outcomes of inhalation bioassays and development of nonsignificant risk levels of exposure are provided. Additionally, justification for the use of inhalation versus noninhalation animal data is provided as is a brief review of human health effects of SVFs. We conclude, inter alia, that Isofrax and Insulfrax have low biodurability, would not be expected to produce either pulmonary fibrosis or lung tumors in a well-designed animal inhalation bioassay, have weighted half-lives beneath the threshold established by the European Union for classification as a carcinogen, and based on epidemiological data for SVFs would not be expected to result in incremental cancer in human cohorts. Finally, it is estimated that approximately 90% of workplace exposure concentrations of these materials would be beneath 1 f/cc. At a concentration of 1 f/cc, neither fiber would be expected to result in an incremental working lifetime cancer risk greater than 10−5.